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---
language: COBOL
contributors:
- ["Hyphz", "http://github.com/hyphz/"]
filename: learn.COB
---
COBOL is a business-oriented language revised multiple times since its original design in 1960. It is claimed to still be used in over 80% of
organizations.
```cobol
*COBOL. Coding like it's 1985.
*Compiles with GnuCOBOL in OpenCobolIDE 4.7.6.
*COBOL has significant differences between legacy (COBOL-85)
*and modern (COBOL-2002 and COBOL-2014) versions.
*Legacy versions require columns 1-6 to be blank (they are used
*to store the index number of the punched card..)
*A * in column 7 means a comment.
*In legacy COBOL, a comment can only be a full line.
*Modern COBOL doesn't require fixed columns and uses *> for
*a comment, which can appear in the middle of a line.
*Legacy COBOL also imposes a limit on maximum line length.
*Keywords have to be in capitals in legacy COBOL,
*but are case insensitive in modern.
*First, we must give our program ID.
*Identification division can include other values too,
*but they are comments only. Program-id is mandatory.
identification division.
program-id. learn.
*Let's declare some variables.
data division.
working-storage section.
*Variables are specified by a "picture" - how they should be
*displayed, and variable type is inferred from this.
*The "01" value is the level number which is used for building
*data structures.
01 myname picture xxxxxxxxxx. *> A 10 character string.
01 age picture 999. *> A number up to 3 digits.
01 valx picture 999. *> Another number up to 3 digits.
01 inyear picture s9(7). *> S makes number signed.
*> Brackets indicate 7 repeats of 9,
*> ie a 6 digit number (not an array).
*Now let's write some code.
procedure division.
main-procedure.
*> COBOL is the language that uses DISPLAY instead of PRINT.
*> Note: no full stops after commands. Only after the LAST
*> command.
display "Hello. What's your name?"
*> Let's input a string.
*> If input too long, later characters are trimmed.
accept myname
display "Hello " myname *> We can display several things.
display "How old are you?"
*> Let's input a number.
*> If input too long, EARLIER characters are trimmed.
accept age
display age *> Left-padded to three chracaters with zeroes,
*> because of the defined PICTURE for age.
*> We have two ways of doing a FOR loop.
*> Old style way: doesn't give an index.
perform age times
display "*" with no advancing *> Ie, no newline at end
end-perform
display "." *> Output buffer isn't flushed until newline.
*> New style way: with an index.
perform varying valx from 1 by 1 until valx > age
display valx "-" with no advancing
end-perform
display "."
*> If tests are still good old if tests.
if myname = "Bob" then
display "I don't like Bob."
else
display "I don't know you."
end-if
*> There are two ways of doing subprograms and calling
*> them.
*> The simplest way: a paragraph.
perform subparagraph
*> The complex way, with parameters and stuff.
call "eratosthenes" using age returning valx
display "There were " valx " primes."
stop run.
subparagraph. *> Marks the top of an internal subprogram.
*> Shares variable score with its caller.
*> Read year from system timer.
*> Remember the whole "year 2000 crisis"? The yyyyddd
*> option was added in response to that.
accept inyear from day yyyyddd.
*> We can do math step-by-step like this...
divide 1000 into inyear.
subtract age from inyear.
display "You were born in " inyear "."
*> Or we can just use expressions.
compute inyear = 1970 - inyear.
if inyear >= 0 then
display "When you were " inyear ", " with no advancing
else
display inyear " years before you were born, " with no
advancing
end-if
display "COBOL was the most popular language in the world."
. *> You can put the final . on a new line if it's clearer.
*If we want to use a subprogram, we use literally a subprogram.
*This is the entire program layout, repeated for the
*eratosthenes subroutine.
identification division.
program-id. eratosthenes.
data division.
working-storage section.
*Declare an array.
*We can declare a variable to use as an index for it at the
*same time.
01 sieve pic 9 occurs 999 times indexed by sa, sb.
*> Standard cobol doesn't have a boolean type.
01 pstart pic 999.
01 counter pic 999.
*Our parameters have to be declared in the linkage section.
*Their pictures must match the values they're called with.
linkage section.
01 maxvalue picture 999.
*"using" declares our actual parameter variables.
*"returning" declares the variable value returned at end.
procedure division using maxvalue returning counter.
main-procedure.
display "Here are all the primes up to " maxvalue "."
perform varying sa from 1 by 1 until sa > maxvalue
move 1 to sieve (sa)
end-perform
perform varying sa from 2 by 1 until sa > maxvalue
if sieve(sa) = 1 then
compute pstart = sa + sa
perform varying sb from pstart by sa until sb >
maxvalue
move 0 to sieve(sb)
end-perform
end-if
end-perform
initialise counter *> To zero by default for a number.
perform varying sa from 2 by 1 until sa > maxvalue
if sieve(sa) = 1 THEN
display sa
add 1 to counter
end-if
end-perform.
end program eratosthenes.
end program learn.
```
##Ready For More?
* [GnuCOBOL](https://sourceforge.net/projects/open-cobol/)
|
